Insects and other pests cost farmers billions of dollars annually in crop losses and in the expense of keeping these pests under control. The losses caused by insect pests in agricultural production environments include decrease in crop yield, reduced crop quality, and increased harvesting costs.
Cultivation methods, such as crop rotation and the application of high nitrogen levels to stimulate the growth of an adventitious root system, has partially addressed problems caused by agricultural pests. Economic demands on the utilization of farmland restrict the use of crop rotation. In addition, overwintering traits of some insects are disrupting crop rotations in some areas. Thus, chemical insecticides are relied upon most heavily to guarantee the desired level of control. Insecticides are either banded onto or incorporated into the soil.
The use of chemical insecticides has several drawbacks. Continual use of insecticides has allowed resistant insects to evolve. Situations such as extremely high populations of larvae, heavy rains, and improper calibration of insecticide application equipment can result in poor control. The use of insecticides often raises environmental concerns such as contamination of soil and of both surface and underground water supplies. The public has also become concerned about the amount of residual, synthetic chemicals which might be found on food. Working with insecticides may also pose hazards to the persons applying them. Therefore, synthetic chemical pesticides are being increasingly scrutinized, and correctly so, for their potential toxic environmental consequences. Examples of widely used synthetic chemical pesticides include the organochlorines, e.g., DDT, mirex, kepone, lindane, aldrin, chlordane, aldicarb, and dieldrin; the organophosphates, e.g., chlorpyrifos, parathion, malathion, and diazinon; and carbamates. Stringent new restrictions on the use of pesticides and the elimination of some effective pesticides from the market place could limit economical and effective options for controlling damaging and costly pests.
Because of the problems associated with the use of organic synthetic chemical pesticides, there exists a clear need to limit the use of these agents and a need to identify alternative control agents. The replacement of synthetic chemical pesticides, or combination of these agents with biological pesticides, could reduce the levels of toxic chemicals in the environment.
A biological pesticidal agent that is enjoying increasing popularity is the soil microbe Bacillus thuringiensis (B.t.). The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium. Most strains of B.t. do not exhibit pesticidal activity. Some B.t. strains produce, and can be characterized by, parasporal crystalline protein inclusions. These inclusions often appear microscopically as distinctively shaped crystals. Some B.t. proteins are highly toxic to pests, such as insects, and are specific in their toxic activity. Certain insecticidal B.t. proteins are associated with the inclusions. These “δ-endotoxins” are different from exotoxins, which have a non-specific host range. Other species of Bacillus also produce pesticidal proteins.
Certain Bacillus toxin genes have been isolated and sequenced, and recombinant DNA-based products have been produced and approved for use. In addition, with the use of genetic engineering techniques, new approaches for delivering these toxins to agricultural environments are under development. These include the use of plants genetically engineered with toxin genes for insect resistance and the use of stabilized intact microbial cells as toxin delivery vehicles. Thus, isolated Bacillus toxin genes are becoming commercially valuable.
Until the last fifteen years, commercial use of B.t. pesticides has been largely restricted to targeting a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis subsp. kurstaki have been used for many years as commercial insecticides for lepidopteran pests. For example, B. thuringiensis var. kurstaki HD-1 produces a crystalline δ-endotoxin which is toxic to the larvae of a number of lepidoteran insects.
In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely israelensis and morrisoni (a.k.a. tenebrionis, a.k.a. B.t. M-7, a.k.a. B.t. san diego), have been used commercially to control insects of the orders Diptera and Coleoptera, respectively. Bacillus thuringiensis var. tenebrionis has been reported to be active against two beetles in the order Coleoptera (Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni).
More recently, new subspecies of B.t. have been identified, and genes responsible for active δ-endotoxin proteins have been isolated. Höfte and Whiteley classified B.t. crystal protein genes into four major classes (Höfte, H., H. R. Whiteley [1989] Microbiological Reviews 52(2):242–255). The classes were CryI (Lepidoptera-specific), CryII (Lepidoptera- and Diptera-specific), CryIII (Coleoptera-specific), and CryIV (Diptera-specific). The discovery of strains specifically toxic to other pests has been reported. For example, CryV and CryVI have been proposed to designate a class of toxin genes that are nematode-specific.
The 1989 nomenclature and classification scheme of Höfte and Whiteley for crystal proteins was based on both the deduced amino acid sequence and the host range of the toxin. That system was adapted to cover 14 different types of toxin genes which were divided into five major classes. The number of sequenced Bacillus thuringiensis crystal protein genes currently stands at more than 50. A revised nomenclature scheme has been proposed which is based solely on amino acid identity (Crickmore et al. [1996] Society for Invertebrate Pathology, 29th Annual Meeting, IIIrd International Colloquium on Bacillus thuringiensis, University of Cordoba, Cordoba, Spain, Sep. 1–6, 1996, abstract). The mnemonic “cry” has been retained for all of the toxin genes except cytA and cytB, which remain a separate class. Roman numerals have been exchanged for Arabic numerals in the primary rank, and the parentheses in the tertiary rank have been removed. Many of the original names have been retained, with the noted exceptions, although a number have been reclassified.
Many other B.t. genes have now been identified. WO 94/21795, WO 96/10083, WO 98/44137, and Estruch, J. J. et al. (1996) PNAS 93:5389–5394 describe Vip1A(a), Vip1A(b), Vip2A(a), Vip2A(b), Vip3A(a), and Vip3A(b) toxins obtained from Bacillus microbes. Those toxins are reported to be produced during vegetative cell growth and were thus termed vegetative insecticidal proteins (VIP). Activity of these toxins against certain lepidopteran and certain coleopteran pests was reported. WO 98/18932 discloses new classes of pesticidal toxins.
Obstacles to the successful agricultural use of Bacillus toxins include the development of resistance to B.t. toxins by insects. In addition, certain insects can be refractory to the effects of Bacillus toxins. The latter includes insects such as boll weevil and black cutworm as well as adult insects of most species which heretofore have demonstrated no apparent significant sensitivity to B.t. δ-endotoxins. While resistance management strategies in B.t. transgene plant technology have become of great interest, there remains a great need for developing additional genes that can be expressed in plants in order to effectively control various insects.
The subject application provides new classes of toxins and genes, in addition to those described in WO98/18932, and which are distinct from those disclosed in WO 94/21795, WO 96/10083, WO 98/44137, and Estruch et al.